318 HISTOGENESIS 



scattered through the mantle and marginal layers of the neural tube. By pro- 

 liferation they increase in numbers and their form depends upon the pressure 

 of the nerve cells and fibers which develop around them. 



Neuroglia fibers are differentiated from the cytoplasm and cytoplasmic 



Fig. 305. — Ependymal cells of the lumbar cord from a human embryo of 44 mm. Golgi method 

 (Cajal). A, floor plate; B, central canal; C, line of future fusion of walls of neural cavity; D, 

 neuroglia cells and fibers. 



processes of the neuroglia cells, and as the latter primarily form a syncytium, the 

 neuroglia fibers may extend from cell to cell. The neuroglia fibers develop late 

 in fetal life and undergo a chemical transformation into neurokeratin, the same 

 substance which is found in the sheaths of medullated fibers. 



